Monday 25 October 2010 09.30 EDT
First published on Monday 25 October 2010 09.30 EDT

There is quite a lot that could be said about anyone who converts to Islam in Iran under the impression that it is less inhumane than New Labour, but as a piece of theatre, described in William James, and central both to evangelical Christianity and Alcoholics Anonymous. But it is also always a political and social act, a statement about where you fit into the world. To convert is to announce your allegiance to a new tribe, or a new idea of humanity.

It is also, by implication at least, a rejection of your old self, and of the people who thought they recognised you in it. In this it is more like a divorce or a remarriage than any kind of intellectual experience. This is why it is a little silly to mock Lauren Booth for saying she has got up to page 60 of the Qur'an, after reading it every day. The conviction precedes the reading, and drives it along. Besides, how fast are you supposed to read a holy book? It's not as if you're trying to discover who dun it, only how He did it, and that is a study which can take a very long time. I might think her more sincere if she announced she was still on page one after three months.

But leave God out of this for the moment. Conversion always involves a conversation with the people around you, and just as with any other conversation, the meaning depends on where you are. To become a Muslim in Britain is a very different thing to becoming one in Indonesia, and in Argentina it's different again. This has absolutely nothing to do with doctrine. Baptists in the southern US can believe almost exactly the same things as Baptists in the Ukraine, but in one case baptism means you are becoming a normal person, and in the other that you are defining yourself as a weirdo.

In theory, all of the monotheistic religions try to stress the way in which true conversion moves you away from worldly things and into a relationship with God, rather than one with society. But in practice, most of the time, most people find their theological beliefs are a way of expressing their relationship with society. Disraeli could never have become prime minister had his father not converted from Judaism to Christianity. Even within Christianity, Margaret Thatcher found it necessary as part of her social rise to move from Methodism to Anglicanism.

To convert to Islam in a British prison is one way of expressing your disdain for the world outside, whereas conversion to Christianity is an attempt to come to terms with the dominant culture. To proclaim yourself an atheist in some parts of America is to invite derision, as much as it would be to announce in the BBC that you were a practising Calvinist.

Of course the consequence of conversion can be very much worse than derision. In almost all countries there is some religion that is regarded as treacherous almost in its essence. Much of the present tension in the US over Cordoba House comes from the attempts to define Islam as communism once was – an ideology that is incompatible with patriotism. But at least the American constitution works against such efforts in theory. Had Lauren Booth had a different mystical experience in Iran, and converted away from Islam rather than into it, she would have been liable to the death penalty.